In the early 1970's the first commercial system for condensing hot saturated vapor on articles for the purposes of soldering, brazing, fusing, etc., articles was developed. That system is described in detail in U.S. Pat. No. Re. 30,399 which issued on Sept. 9, 1980 to R. C. Pfahl and H. H. Ammann assigned to Western Electric Company, Inc. and Bell Telephone Laboratories, Inc., and is hereby incorporated by reference herein. That patent discloses an article to be soldered, fused or brazed being placed in a vessel containing a body of hot saturated vapor. The vapor is generated by continuously boiling a heat transfer liquid having selected properties including a boiling point at least equal to and preferably above the temperature of the soldering, fusing or brazing operation to be performed. The vapor condenses on the article and gives up its latent heat of vaporization thereto to heat the article to the temperature required for the particular operation. This technique has found wide acceptance in the industry and has substantially advanced the art of soldering, brazing and fusing.
The Pfahl et al. process was improved to substantially reduce losses of the hot saturated vapor of the relatively expensive heat transfer (primary) liquid by a technique disclosed in U.S. Pat. No. 3,904,102 to T. Y. Chu et al., which issued Sept. 9, 1975 and is assigned to the instant assignee. In Chu et al. a blanket of secondary vapor, from a relatively inexpensive liquid, having a density intermediate that of the relatively expensive primary heat transfer vapor and the atmosphere, floats on the body of primary vapor in order to reduce the losses thereof from a condensation heating vessel.
The article on which the soldering, fusing or brazing operation is to be performed is passed through the body of secondary vapor into the body of primary vapor in the vessel. The primary vapor condenses on the article and the latent heat of vaporization of the condensing primary vapor heats the article to the temperature required for the soldering, fusing or brazing operation. After completion of the operation, the article is withdrawn from the body of primary vapor, through the blanketing body of secondary vapor, out of the vessel and into the atmosphere where it is cooled to ambient temperature. As the article moves out of the vessel, vapor is also dragged out and lost to the atmosphere. Most of the vapor is secondary, however, some is the relatively expensive primary vapor.
One technique designed to lessen such vapor losses is described in U.S. Pat. No. 4,264,299 which issued on Apr. 28, 1981 to H. H. Ammann et al., which is incorporated herein by reference. That patent discloses a condensation heating facility having a primary vapor chamber with a drying chamber located thereabove. The drying chamber has first and second doors in the top and bottom portions thereof, respectively. Articles to be soldered are conveyed into the drying chamber through the first door and then into the primary vapor chamber, through the second door, where the soldering, fusing or brazing operation takes place. The articles are then removed to the drying chamber, the first and second doors are closed, and drying apparatus activated to remove and filter out any primary vapor therein. The first door is then opened and the dry, soldered articles removed from the facility.
The Ammann et al. patent has been found effective for soldering articles in a closed, single vapor condensation heating facility which substantially reduces loss of the expensive primary vapor to the atmosphere. However, the various conveying mechanisms required to transport articles through the facility are complex. Therefore, the drying chamber cannot be completely sealed during the drying operation. Additionally, the conveying mechanisms passing through the facility substantially increase the size of the machine because of the horizontal and vertical movement of parts required.
Accordingly, there is a need for a simple and effective technique for loading and removing articles from a single vapor condensation heating facility while providing substantially complete sealing of the drying chamber during the drying operation.